1. Field of the Invention
The present invention concerns flow control. It has particular, although not exclusive, application to automatic selection among multiple flow states.
2. Background Information
Fluid flow has been controlled automatically in a wide range of applications for over a century, and electrically operated valves have been employed in most cases. Yet there are a number of applications in which conversion of flow control from previously manual operation to automatic operation has become popular only in recent years. Examples are object-sensor-controlled faucets and flushers employed in public restrooms. Because of advances in control-logic circuitry and in valve-operator efficiency, it has become practical to extend automatic flow control to such applications, where cost considerations would previously have ruled out their use.
While such market penetration is a testament to advances in these technologies, cost and power considerations still remain limiting factors in some contexts. In some cases, for example, the flow-control systems must be powered by batteries and achieve battery life on the order of several years. Clearly, energy constraints are severe in such applications. And, while significant further reductions in the cost of logic circuitry can be expected, the energy requirements and capital cost of (typically solenoid-actuated) electrical valves are likely to fall much more slowly. So the valve actuator will be a significant contributor not only to a flow-control system""s initial cost but also to its power consumption, and it can thus determine whether automatic operation is practical in a given application.
In the case of multi-way flow systems, one approach to containing that element of system cost is exemplified by the arrangement that U.S. Pat. No. 5,727,591 to Doll illustrates. In that arrangement, a simple two-state actuator operates a reciprocation-stepper mechanism. Such a mechanism, of which perhaps the most familiar example is the advance/retract mechanism in retractable ball-point pens, is operated by advancing and retracting its reciprocation member, e.g., a pen""s operator button. Repeated reciprocation of that member causes an indexing member (which may be the same as the reciprocation member) to advance through a sequence of index positions. In the case of the ball-point pen, advancing through the sequence yields only two different pen states, one in which the pen is extended and the other in which it is retracted. In the Doll arrangement, though, the index member is advanced through states in which it offers three different levels of resistance to fluid flow.
While the Doll arrangement does provide a way of using a simple two-state actuator to select among a greater number of flow states, it turns out that the resultant savings are largely illusory. Although that arrangement uses only a single such actuator, the size and power that its solenoid requires tend to be high if significant flow rates or high pressures are to be controlled.
We have developed a way of reducing the portion of system cost that the electrical valve actuator tends to contribute when the system needs to choose among more than two flow states. According to our invention, a manifold forms a manifold chamber and a plurality of ports that afford access to the manifold chamber. The reciprocation stepper""s reciprocation member is so exposed to the manifold chamber""s pressure that it tends to be urged thereby to an extended reciprocation state when the manifold-chamber pressure is elevated. The pressure of the fluid being controlled can therefore be enlisted to operate the reciprocation member, and power needs to be expended only to control the admission of pressurized fluid into chamber. That is, one of the ports is a control port, and a valve used to control flow through the control port can thereby control the reciprocation member""s reciprocation state.
Now, the pressure of the controlled fluid has been used for this purpose before; U.S. Pat. Nos. 4,448,476 to Diel et al. and 4,744,285 to Presley describe examples. But we have recognized that the advantage of using the fluid""s pressure to operate the reciprocation member can be obtained without the complicated arrangements to which those approaches resort. Although those approaches do advance and retract the reciprocation member by alternately pressurizing and relieving pressure in the ported manifold chamber, they need multi-way valves to redirect the pressurized fluid alternately to opposite sides of the reciprocation member. We instead bias the reciprocation member to a relaxed reciprocation state so that a simple two-state valve can control the reciprocation state; pressure does not have to be controlled on both sides of the reciprocation member.
The two-state control valve may, for example, alternately maintain and relieve pressure communicated into the manifold chamber by one or more other, controlled ports. The reciprocation member""s bias will cause it to assume a relaxed state when the control valve is open and thereby relieves the chamber pressure, and the high chamber pressure that results when the control valve is closed will cause that member to assume an extended state. As will be explained below, this toggling between states causes the index member to advance through positions in which it causes different flow states among the manifold ports. Use of a two-state control valve for this purpose affords the potential for very low capital cost and energy use.